The emergence of hyperthermia as a cancer therapy has been an exciting clinical development even though its potential is still unknown. One of the main problems has been correlating the observed tumor response with the temperature distributions achieved during treatment. Lack of knowledge of complete temperature distributions within the target tissue volume has lead to confusing and conflicting results which will ultimately be used to draw conclusions about hyperthermia as a clinical cancer therapy if treatment monitoring capabilities are not improved. The principal hypothesis of the proposed work is that electrical impedance changes recorded f=during hyperthermia cancer treatment are indicators which can be used to improve the monitoring and assessment of therapy delivery. To evaluate this hypothesis, electrical impedance imaging (EIT) techniques will be used to estimate temperature distributions through differential changes in reconstructed impedance profiles which will be correlated to temperature rise through empirical relationships and directly measured temperature data. While EIT is generally viewed as an imaging modality of low resolution and moderate sensitivity, the approach taken in this research counteracts some of these limitations by using internal measurements and other a priori data along with sophisticated reconstruction algorithms based on the finite element method. A prototype EIT imager has been developed and preliminary results obtained during phantom heating experiments have been promising and have suggested that temperature sensitivities on the order of 0.5 degrees Celsius are achievable in a practical setting. The research proposed as part of this project focuses on the realization of a second generation system which involves several significant hardware and software advancements including 3D imaging capabilities. Extensive in vitro and in vivo testing a of these improvements will be conducted to quantify overall system performance and potential as a thermal imaging technique for estimating temperature fields during hyperthermia delivery. If the objectives of this project can be met a valuable tool for providing desperately needed thermal data on clinically induced hyperthermia will have been realized. With the knowledge of complete temperature distributions that appears possible using EIT, relationships between therapeutic outcome and variation in tumor temperature distributions can be determined. Then, the sensitivity of the desired temperature profile to controllable treatment parameters can be systematically studied and treatment protocols which maintain a high likelihood of achieving the desired response can be developed and the efficacy of hyperthermia established based on a strong clinical rationale.